This invention relates to improved apparatus and methods for supplying carbon to the electrolytic cells used in the production of aluminum metal.
In the present processes for the production of aluminum by electrolytic reduction of aluminum compounds, especially alumina, in a molten salt (especially cryolite) bath, the carbon anodes are gradually consumed, and must be periodically replaced, which entails substantial costs of labor and lost production time associated with the shutdown and startup necessitated by the anode replacement procedure. Moreover, the anode preparation, involving the use of special binders and baking procedures, adds substantially to the overall cost of aluminum production.
Attempts to develop permanent anodes of conductive oxide materials have failed because of the tendency of the oxides to dissolve in molten cryolite. Furthermore, a permanent anode which would not react with oxygen would necessitate a higher voltage input and hence a higher electrical energy consumption than the present anodes in which the reaction of carbon with oxygen helps to reduce the voltage and energy requirements.